import JSEncrypt from 'jsencrypt'
import { parseBigInt } from 'jsencrypt/lib/lib/jsbn/jsbn'

function pkcs1unpad2(d, n) {
    var b = d.toByteArray()
    var i = 0
    while (i < b.length && b[i] === 0) {
        ++i
    }
    // if (b.length - i !== n - 1 || b[i] !== 2) {
    //   return null
    // }
    ++i
    while (b[i] !== 0) {
        if (++i >= b.length) {
            return null
        }
    }
    var ret = ''
    while (++i < b.length) {
        var c = b[i] & 255
        if (c < 128) { // utf-8 decode
            ret += String.fromCharCode(c)
        } else if ((c > 191) && (c < 224)) {
            ret += String.fromCharCode(((c & 31) << 6) | (b[i + 1] & 63))
            ++i
        } else {
            ret += String.fromCharCode(((c & 15) << 12) | ((b[i + 1] & 63) << 6) | (b[i + 2] & 63))
            i += 2
        }
    }
    return ret
}

export function decrypt(data, publicKey) {
    const encrypt = new JSEncrypt()
    encrypt.setPublicKey(publicKey)
    // 不支持公钥解密
    // 自定义解析方法支持公钥解析
    const rsaKey = encrypt.getKey()
    rsaKey.decrypt = function(ctext) {
        var c = parseBigInt(ctext, 16)
        var m = this.doPublic(c)
        if (m == null) {
            return null
        }
        return pkcs1unpad2(m, (this.n.bitLength() + 7) >> 3)
    }
    return encrypt.decrypt(data)
}
